In many medical conditions, it is necessary to drain or empty internal body cavities of liquids, e.g., urine, blood, etc. For this purpose, numerous designs of catheters are available and commonly used. If it is required that the drainage be performed over an extended period of time, such as several days, weeks or even months, it is essential that the catheter be properly secured inside the body cavity that is being drained. One common type of securable catheter is known as a Cope loop catheter or lockable “pig-tail” catheter. This catheter is characterized by including a means to form a curl (i.e., pig-tail) at its distal end once the catheter has been positioned inside the body cavity, thereby forming an efficient means to prevent or resist the catheter from being pulled out. For example, the curl can be formed by pulling a thread that is secured at the proximal end of the catheter and runs inside the catheter lumen to its distal tip, where it exits through an exit hole located in the vicinity of the catheter tip. The thread runs back along the outer surface of the catheter, enters the catheter again through a hole at a certain distance from the distal exit hole, and then passes inside the catheter to the proximal end of the catheter, where a “loose end” of the thread is available for a physician to grip and pull. Pulling the thread causes the two distally located holes to approach each other, thereby forming the curl.
Percutaneous nephrostomy is one of the oldest techniques used in interventional radiology. It comprises placing a drainage catheter or tube inside the renal pelvis through a skin insertion. The drainage catheter used for percutaneous nephrostomy typically is the “Cope loop” type drainage catheter described above. Early methods were very time consuming, requiring multiple procedural steps. In fact, the procedure could take up to a week to complete. However, the technique has been developed substantially and today the entire procedure is performed at one time in one continuous sequence of steps.
Despite the many advantages of the Cope loop catheter, in particular its very efficient locking function by virtue of the curl, it nevertheless still has certain disadvantages. For example, one problem with the Cope loop catheter is the potential difficulty in creating the desired loop, especially in an undilated system. In particular, the catheter tip sometimes gets stuck in a calyx or in the ureter and may require substantial manipulation before a locking curl is obtained.
Furthermore, because urine is a supersaturated solution of salts, the salt is easily crystallized from the solution when the solution comes into contact with a foreign material, such as the catheter material. If this happens, the catheter clogs and, because the pulling thread runs inside the lumen of the catheter, the thread may get stuck in the precipitated crystals. In this situation, it may be very difficult, if not impossible, to manipulate the locking thread to remove the curl and “unlock” the catheter. As a consequence, the physician may need to perform a more complicated and invasive intervention to remove the catheter.